patch 8.2.1795: Vim9: operators && and || have a confusing result

Problem:    Vim9: operators && and || have a confusing result.
Solution:   Make the result a boolean.

runtime/doc/vim9.txt

@@ -154,25 +154,25 @@ Functions and variables are script-local by default ~
 							*vim9-scopes*
 When using `:function` or `:def` to specify a new function at the script level
 in a Vim9 script, the function is local to the script, as if "s:" was
-prefixed.  Using the "s:" prefix is optional.  To define or use a global
-function or variable the "g:" prefix should be used.  For functions in an
-autoload script the "name#" prefix is sufficient. >
+prefixed.  Using the "s:" prefix is optional.  To define a global function or
+variable the "g:" prefix must be used.  For functions in an autoload script
+the "name#" prefix is sufficient. >
 	def ThisFunction()          # script-local
 	def s:ThisFunction()        # script-local
 	def g:ThatFunction()        # global
-	def ThatFunction()          # global if no local ThatFunction()
 	def scriptname#function()   # autoload
 
-When using `:function` or `:def` to specify a new function inside a function,
-the function is local to the function.  It is not possible to define a
-script-local function inside a function. It is possible to define a global
-function, using the "g:" prefix.
+When using `:function` or `:def` to specify a nested function inside a `:def`
+function, this nested function is local to the code block it is defined in.
+In a `:def` function IT is not possible to define a script-local function.  it
+is possible to define a global function by using the "g:" prefix.
 
 When referring to a function and no "s:" or "g:" prefix is used, Vim will
 prefer using a local function (in the function scope, script scope or
-imported) before looking for a global function.
-In all cases the function must be defined before used.  That is when it is
-first called or when `:defcompile` causes the call to be compiled.
+imported) before looking for a global function.  However, it is recommended to
+always use "g:" to refer to a local function for clarity.  In all cases the
+function must be defined before used.  That is when it is first called or when
+`:defcompile` causes the call to be compiled.
 
 The result is that functions and variables without a namespace can usually be
 found in the script, either defined there or imported.  Global functions and
@@ -184,7 +184,7 @@ and cannot be deleted or replaced.
 
 
 Variable declarations with :var, :final and :const ~
-							*vim9-declaration*
+						*vim9-declaration* *:var*
 Local variables need to be declared with `:var`.  Local constants need to be
 declared with `:final` or `:const`.  We refer to both as "variables" in this
 section.
@@ -261,7 +261,7 @@ Example: >
 	myList = [3, 4]		# Error!
 	myList[0] = 9		# Error!
 	muList->add(3)		# Error!
-
+<							*:final*
 `:final` is used for making only the variable a constant, the value can be
 changed.  This is well known from Java.  Example: >
 	final myList = [1, 2]
@@ -471,10 +471,6 @@ Conditions and expressions are mostly working like they do in JavaScript.  A
 difference is made where JavaScript does not work like most people expect.
 Specifically, an empty list is falsy.
 
-Any type of variable can be used as a condition, there is no error, not even
-for using a list or job.  This is very much like JavaScript, but there are a
-few exceptions.
-
 	type		TRUE when ~
 	bool		v:true or 1
 	number		non-zero
@@ -490,17 +486,25 @@ few exceptions.
 	class		when not NULL
 	object		when not NULL (TODO: when isTrue() returns v:true)
 
-The boolean operators "||" and "&&" do not change the value: >
-	8 || 2   == 8
-	0 || 2   == 2
-	0 || ''  == ''
-	8 && 2   == 2
-	0 && 2   == 0
-	2 && 0   == 0
-	[] && 2  == []
+The boolean operators "||" and "&&" expect the values to be boolean, zero or
+one: >
+	1 || false   == true
+	0 || 1       == true
+	0 || false   == false
+	1 && true    == true
+	0 && 1       == false
+	8 || 0	     Error!
+	'yes' && 0   Error!
+	[] || 99     Error!
 
-When using `..` for string concatenation arguments of simple types are always
-converted to string. >
+When using "!" for inverting, there is no error for using any type and the
+result is a boolean: >
+	!'yes'	    		== false
+	var myList = [1, 2, 3]
+	!!myList    		== true
+
+When using "`.."` for string concatenation arguments of simple types are
+always converted to string. >
 	'hello ' .. 123  == 'hello 123'
 	'hello ' .. v:true  == 'hello v:true'